Tanya Degurechaff is a young soldier infamous for predatorial-like ruthlessness and an uncanny, tactical aptitude, earning her the nickname of the "Devil of the Rhine." Underneath her innocuous appearance, however, lies the soul of a man who challenged Being X, the self-proclaimed God, to a battle of wits—which resulted in him being reincarnated as a little girl into a world of magical warfare. Hellbent on defiance, Tanya resolves to ascend the ranks of her country's military as it slowly plunges into world war, with only Being X proving to be the strongest obstacle in recreating the peaceful life she once knew. But her perceptive actions and combat initiative have an unintended side effect: propelling the mighty Empire into becoming one of the most powerful nations in mankind's history.
[Written by MAL Rewrite]

Kana is a 17-year-old high school junior who spends her days hanging out with her besties, Mossan, Hijiri, and Pets. They live unremarkable lives, until the day a Mecha falls out of the sky, along with a strange woman named Haruko. Her plans for Kana and her friends involve the force known as ATOMSK. Kana will have to risk everything to decide whether or not to help... like she really has a choice!
(Source: Adult Swim)

In 1926, Tanya and her battalion return home from defeating remnants of the Republic's army. However, when they arrive they receive word of a massive mobilization near the border with the Russy Federation, so the Empire's army must prepare. At the same time, a multinational army under the leadership of the Allied Kingdom moves into the Russy Federation. The enemy of an enemy is a friend, but among the Allied Kingdom army is Mary Sioux, a girl who has sworn to exact justice against the Empire for the death of her father.
(Source: ANN)